There were. They just happened to have died out. So, ancient native Americans, potentially horse-knowledgeable, and then they died out 10000 or so years ago.
Which is an even weirder and more fun fact, an addendum fact.
There were no horses in America, there were evolutionary ancestors of horses that would not be able to fulfill any horse role.
Just like zebras are not horses and wolves not dogs. They would obviously not be owned by Native Americans nor would the Native Americans have a remarkable body of knowledge about them (like they developed with actual horses).
Horses were bred to be big and strong enough in Central Asia.
We also learned about horses in America from the book of Mormon. They were also around approximately 2 - 3,000 years ago before all the good light skinned believers died out. Along with their horses...
Weird less fun non fact addendum to the weird fun addendum fact.
In the same way that man wasn't drastically different evolution wise from that period to now (science says we got a little shorter, but thats about it genetically) , horses were not some wild precursor species here. They were just horses. Potentially stockier, but still horses
Stupid argument. Slective breeding has taken place for all of history, the beasts in your mideval paintings are no more Cats than they are unnatural felines.
Evolution takes a long time, the banana you're talking about isn't the same banana from 100 years ago, it's a straight up different strain that grew/evolved parallel to the banana your great grandparents used to buy at the store. So, no, it's not the same banana DNA wise, but it's also not even the same banana strain. It's like you're pointing at Zebras and saying they're not horses, we all already knew that part. But if a cave painting from 2000 years ago depicts a Quagga, we can all just go ahead and say 'ancient Zebras' and colloquially no one will be upset.